1. Field of the Invention
The invention relates to a method and device capable of simultaneously creating a series of identical micro-arrays, each micro-array comprising hundreds or thousands of analyte-assay regions on a solid support, each analyte-specific reagent useful, for example, in detecting labeled cDNA in hybridization assays.
2. Description of the Related Art
Micro-arrays of hundreds or thousands of biological analyte-assay regions are widely used for biological analysis. Tiny droplets, each containing a different known reagent, usually distinct polynucleotide or polypeptide biopolymers such as known DNA fragments, are deposited and immobilized in a regular array on a solid substrate such as a glass microscope slide. The array of dried droplets is exposed to a solution containing an unknown, for example complementary DNA (cDNA) fragments pre-labeled with fluorescent or radioactive chemical tags. Binding reactions or hybridizations occur wherever there is a match between the complementary sequence polynucleotides in the array and the cDNA. Subsequent optical or radiosensitive scanning determines which spots contain tags, thereby identifying the complementary compounds present in the solution.
While micro-arrays provide a useful tool for rapid biological analysis, the processes by which the micro-arrays are produced remain time consuming and expensive.
For example, it is known from U.S. Pat. No. 5,807,522 (Shalon et al.) to use capillary pens of various geometries to print or spot droplets onto substrates, one substrate at a time. Although multiple (typically 8 or 16) pens may be used simultaneously, often under robotic control, each pen or group of pens is loaded with only one reagent per pen. The pen(s) are then touched to one substrate after another, depositing nearly identical droplets on each. After each of the set of substrates to be prepared (typically a few dozen to several hundred) has been spotted with a first set of reagent droplets, the set of pens is washed and dried, reloaded with the next set of reagents and the next set of droplets are printed onto the same substrates at adjacent locations. This procedure is time consuming and requires expensive and elaborate equipment to achieve precision and speed.
Another known method involves long flexible capillary tubes to carry fluid from sets of storage wells to the tips of the tubes, which tips are applied to one substrate after another in a manner similar to Shalon et al. This method suffers all of the same disadvantages as Shalon et al. and also requires a significant volume of expensive reagent to be stored in the capillary tubes.
Still another known method is disclosed in U.S. Pat. No. 5,800,992 (Fodor et al.) and involves combinatorial chemistry to synthesize oligonucleotides on the substrate with a series of chemical reactions (Affymetrix). This method is limited to oligonucleotides and is not suitable for long stranded cDNA's. In addition, the sequence of the oligonucleotides must be known in advance. This method also suffers the disadvantages of requiring cumbersome expensive equipment and involving time consuming reaction steps.
In order to amplify the fluorescence or radioactivity signal indicative of a binding reaction, U.S. Pat. No. 5,843,767 (Beattie) teaches the provision of a multiplicity of discrete channels running through the substrate and arranged in groups, and with binding reagent immobilized on the walls of the channels. The channels increase the amount of surface area in the substrate available for the binding, thus theoretically improving detection sensitivity and efficiency. However, in practice, it has been found that the improvements were not as great as expected, since the detection optics will still be limited to direct reception only from the projected area.